1. Field of the Invention
The present invention generally relates to a power supply apparatus, and more particularly, to a power supply apparatus which offers a power isolation function to prevent reverse current.
2. Description of Related Art
In a high-end electronic product (for example, a server or an industrial computer), two power suppliers of the same specifications and both offering a negative feedback control function are usually connected in parallel for supplying electric power required by the operation of the electronic product (i.e., a load). In this case, an output isolation switch-component (for example, a metal-oxide-semiconductor field-effect transistor (MOSFET)) is disposed on the output path of each power supplier. The output isolation switch-component is turned on by a comparator when the output current of the power supplier forwardly flows to the load and turned off when a reverse current flows to the power supplier. Thereby, an output power isolation is achieved.
However, to meet today's requirement for high efficiency, an output isolation switch-component is usually implemented by using a MOSFET with low conductive impedance (Rds-on). Accordingly, the voltage drop on the output isolation switch-component (i.e., the voltage difference between the drain and the source of a MOSFET) is very small.
Moreover, the comparator controlling the on/off of an output isolation switch-component may produce offset errors. As a result, the comparator may not be able to determine the voltage difference on the output isolation switch-component correctly when the load is a light load (because in this case the output current of the power supplier is small). Accordingly, the comparator may not be able to turn off the output isolation switch-component (MOSFET) when a reverse current flows to the power supplier. Instead, the comparator turns off the output isolation switch-component (MOSFET) only when the reverse current is large enough. Thus, the power supplier may be damaged or may malfunction due to the large reverse current.
Thereby, with today's requirement for high efficiency, the conventional output power isolation technique cannot effectively resolve the problem produced when a reverse current flows to a power supplier under the load is a light load.